Method of manufacturing bipolar device and structure thereof

ABSTRACT

Disclosed are a method for forming a base layer by epitaxial growth technology of a heterojunction bipolar device and a structure of the bipolar device manufactured by the method. The method comprises steps of depositing an insulation film containing silicon nitride on a substrate and removing a part of the insulation film to define a collector area; growing a first semiconductor in the collector area by selective epitaxial growth method to form the collector protruded over the insulation film in the form of a mushroom; forming an oxide film containing silicon dioxide on a surface of the collector protruded over the silicon nitride; selectively growing a second polycrystalline semiconductor material on only the nitride insulation film at the same height as the protruded portion of the collector to form a first base semiconductor electrode; removing an upper surface of the oxide film to expose the collector; and growing a second semiconductor containing silicon-germanium on the second polycrystalline semiconductor and the collector of the first semiconductor to form a second base semiconductor electrode on the first base semiconductor electrode and the base on the collector, thereby preventing a current leakage and a loading effect.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method of manufacturing asilicon-germanium heterojunction bipolar transistor (SiGe HBT) and astructure thereof, and more particularly, to a method of forming a baselayer including silicon-germanium by epitaxial growth and a structure ofthe SiGe HBT in a heterojunction bipolar transistor used as a high-speeddevice.

[0003] 2. Description of the Related Art

[0004] Presently, due to continuous research and development in thefield of electronics and telecommunications, optical transmission at atransmission rate of 10 Gbps or more is practicable using a high-speeddevice of 60 GHz class or more. In near future, it is expected that a20˜30 Gbps IC for the optical transmission will be developed using thehigh-speed device of 100 GHz and an optical transmission system of fewhundred Gbps class will be commercialized. In the field of a mobilecommunication, a terminal is essentially required to be much smaller,lighter, and, as the same time, multi-functionalized with lower powerconsumption. Therefore, RF (radio frequency) components, which are largein their size, should be formed into an IC. By a development of hybridIC technology and MMIC (monolithic microwave integrated circuit)technology, the RF components may be formed into the IC, and the qualityof the terminal and system is improved.

[0005] As one of the silicon bipolar devices, the SiGe HBT in whichsilicon-germanium is used as a base layer has a high operating speed of100 GHz or more, and is in the limelight as an advanced high-speeddevice. The SiGe HBT device employs almost all the existing siliconprocess as it is and forms the base layer having a thin thickness of0.02 μm with the silicon-germanium using the epitaxial growth. Since thebase layer (about 0.02 μm) is thinner than that of a conventionaljunction transistor and is formed by epitaxial growth usingsilicon-germanium having a smaller band gap than silicon, there is someadvantage to obtain a high current gain and operating speed with lowerpower consumption.

[0006] A conventional method of manufacturing the SiGe HBT and structurethereof is as follows. FIG. 1 shows a cross-sectional view of aconventional heterojunction transistor defining a collector area byLOCOS (local oxidation of silicon) method.

[0007] Ion-implanting an n-type impurity in a p-type silicon substrate 1forms a buried collector 11. Depositing n-type silicon on an entiresurface of the substrate, in which the buried collector is formed, formsa collector thin film. On the collector thin film, an anti-oxidizinginsulation film used as a mask covers a collector area and a collectorsinker area. Then, the silicon exposed through the mask is oxidized bythe LOCOS method to form a collector insulation film 17. Therefore, on aportion of the buried collector 11, the collector thin film except theactive collector region and the collector sinker area is formed into thecollector insulation film (field oxide film) 17 formed of silicondioxide. An n-type impurity is implanted in the collector sinker areaand then heat-treated at a high temperature to form a collector sinker13. A silicon-germanium thin film for forming the base is grown on theentire surface of the substrate and is then patterned, except for thecollector 15 and a portion of the collector insulation film 17 aroundthe collector 15 so as to form a base thin film. Formed on the collector15, is a single crystal base 25. The base 25 is extended laterally onthe collector insulation film 17. The base 25 on the collectorinsulation film 17 is formed into a polycrystalline or amorphous basesemiconductor electrode 23. On the entire surface, there is depositedsilicon dioxide or silicon nitride to form an emitter insulation film37. The emitter insulation film 37 is patterned so as to be opened aportion thereof corresponding to an active area of the base (25),thereby defining an emitter area. On the entire surface of thesubstrate, there is an emitter electrode 39 formed of a polycrystallinesilicon containing the n-type impurity such as arsenic and phosphorus,and so forth. Then, the emitter semiconductor electrode 39 isheat-treated to diffuse the n-type impurity on the base thin film andthus form an emitter 35. The silicon dioxide or the silicon nitride isdeposited on the entire surface of the substrate to form a protectingfilm 77. The protecting film 77 is patterned to form a contact windowfor exposing the emitter 35. Further, the protecting film 77 and theemitter insulation film 37 are patterned to form the contact windows forexposing the base semiconductor electrode 23 and the collector sinker13. Finally, a metal layer is deposited and then patterned to form abase terminal 81 contacted through the contact window with the basesemiconductor electrode 23, an emitter terminal 83 contacted through thecontact window with the emitter 35 and a collector terminal contactedthrough the contact window with the collector sinker 13 (FIG. 1).

[0008] In the LOCOS method as described above, between the collectorinsulation film containing the silicon dioxide and the collector areacontaining the n-type impurity, a clean film is formed without anycrystal defect. However, during the local oxidation of a part of thesilicon layer, a bird's beak is formed at a side of the boundarysurface. The protruding portion acts as an obstacle to scaling down thedevice. Further, when the silicon-germanium thin film grows on thesubstrate of the silicon dioxide film (collector insulation film) andthe silicon (collector), there is a problem that the silicon-germaniumthin film grows selectively on the silicon portion of the substrate.

[0009] In order to solve the problem, there is provided a selectiveepitaxial growth (SEG) method for manufacturing a high density andsub-micron heterojunction transistor. FIG. 2 shows a cross-sectionalview of a structure of a SiGe HBT manufactured by the SEG method. Themanufacturing method will be described more fully.

[0010] Ion-implanting an n-type impurity in a p-type silicon substrate 1forms a buried collector 11. Formed on an entire surface of thesubstrate, on which the buried collector is formed, is a collectorinsulation film 17 of silicon dioxide. After defining a part of thecollector insulation film 17, some portions of the collector insulationfilm 17 corresponding to a collector area and a collector sinker areaare removed so as to expose a portion of the buried collector 11. Apattern shape of the removed collector insulation film 17 is formed tohave a vertical sidewall. The collector area and the collector sinkerarea formed on a surface of the single crystal buried collector exposedthrough the removed portion of the collector insulation film 17 arefilled with the single crystal silicon by the SEG method. At this time,the single crystal silicon excessively grows in the form of a mushroomto be higher than the collector insulation film 17. Then, a protrudedportion of the grown single crystal silicon is removed by achemical-mechanical polishing (CMP) method to flat the surface of thesubstrate. On the substrate on which a collector 15 and a collectorsinker 13 are formed to have a vertical sidewall and a flat surface,silicon-germanium grows to form a base thin film. At this time, singlecrystal silicon-germanium grows on the single crystal silicon, i.e. thecollector 15 to form a base 25 making a junction with the collector 15.Meanwhile, on the collector insulation film 17 formed of the silicondioxide, polycrystalline or amorphous silicon-germanium grow. Formed onthe base thin film is a base ohmic electrode layer 29 of a metalmaterial in order to reduce a contact resistance. A portion of the baseohmic electrode layer 29 corresponding to the base 25 is removed toexpose the base 25. And in order to prevent the base ohmic electrodelayer 29 from being electrically contacted with an emitter to be formed,silicon dioxide or silicon nitride is deposited on the emitterinsulation film 37. Then, the emitter insulation film 37, the base ohmicelectrode layer 29 and the base thin film are patterned to define thebase 25, the base semiconductor electrode 23 and the base ohmicelectrode layer 29. At this time, the collector sinker 13 is exposed.Preferably, on outer sides of the emitter insulation film 37, the baseohmic electrode 29 and the base thin film etched by the patterningprocess, there is formed a sidewall insulation film 97. The emitterinsulation film 37 is patterned so that a portion thereof correspondingto a center portion of the base 25 is removed to expose the base 25.Then, polycrystalline silicon containing an impurity is deposited andpatterned to from an emitter semiconductor electrode 39 contacted withthe exposed base 25 and a collector semiconductor electrode 19 contactedwith the collector sinker 13. By a heat treatment process, the impurityin the emitter semiconductor electrode 39 is diffused to an upperportion of the base 25 to form an emitter 35. The silicon dioxide or thesilicon nitride is deposed on the entire surface of the substrate toform a protecting film 77. The protecting film 77 is patterned to form acontact window for exposing the emitter semiconductor electrode 39. And,the protecting film 77 and the emitter insulation film 37 are patternedto form a contact window for exposing the base ohmic electrode 29. Bysputtering a metal, there are formed a base terminal 81 contacted withthe base ohmic electrode 29, an emitter terminal 83 contacted with theemitter semiconductor electrode 39 and a collector terminal 85 contactedwith the collector semiconductor electrode.

[0011] In the conventional fabricating method described above, there isa problem in the selective epitaxial growth method for forming thecollector 15 and the collector sinker 13. When the single crystalsilicon grows in a well-shaped space having the vertical sidewall formedby the etching process, a boundary surface with the silicon dioxidesidewall has a very rough crystal structure. At the boundary surfacebetween the collector 15 and the collector insulation film 17, there isformed a tunnel through which a carrier is freely passed. As a result,leakage current is generated from the base to the collector area,thereby lowering a quality of a device.

[0012] Further, when manufacturing the heterojunction bipolar device bythe conventional method such as the LOCOS method and the epitaxialgrowth method, there is a problem with growth of the base thin film. Thebase thin film is formed on the collector and the collector insulationfilm by the epitaxial growth. On the surface of the substrate on whichthe crystal growth is performed, there are distributed mainly thesilicon dioxide and intermittently the single crystal silicon area. Inthis situation, if the base thin film grows, it is difficult to form thesilicon germanium thin film, which is uniform in thickness, germaniumcontents, and impurity concentration, due to loading effect. This is aprime cause that the operation speed of the bipolar and quality of theproduct are lowered.

SUMMARY OF THE INVENTION

[0013] Accordingly, it is an object of the present invention to providea heterojunction transistor in which the problems inherent in theconventional transistor manufactured by the selective epitaxial growthmethod proper to reducing of a device size are solved, thereby providinga high operation speed and a high quality of a product, and amanufacturing method thereof.

[0014] It is other object of the present invention to provide a methodof manufacturing a heterojunction bipolar device using thesilicon-germanium as a base layer, which prevents a leakage currentbetween the collector and the base by a defect at a boundary surfacebetween the insulation film and the collector inherent in the selectiveepitaxial growth method, and a structure of the transistor fabricated bythe method.

[0015] It is another object of the present invention to provide afabricating method for reducing the loading effect generated when asemiconductor material containing the SiGe grows on a surface containingthe silicon and the insulation film to form a base layer, and astructure of the transistor fabricated by the method.

[0016] It is yet another object of the present invention to provide amanufacturing method for forming a junction structure between thecollector and the base by a self-aligning method and thus minimizing ajunction parasitic capacitance therebetween, and a structure of abipolar device manufactured by the method.

[0017] According to the present invention, there is provided a method ofmanufacturing a bipolar device, in which a collector, a base and anemitter are formed in order, comprising steps of: depositing aninsulation film containing silicon nitride on a substrate and removing apart of the insulation film to define a collector area; growing a firstsemiconductor in the collector area by selective epitaxial growth methodto form the collector protruded over the insulation film in the form ofa mushroom; forming an oxide film containing silicon dioxide on asurface of the collector protruded over the silicon nitride; selectivelygrowing a second polycrystalline semiconductor material on only thenitride insulation film at the same height as the protruded portion ofthe collector to form a first base semiconductor electrode; removing anupper surface of the oxide film to expose the collector; and growing asecond semiconductor containing silicon-germanium on the secondpolycrystalline semiconductor and the collector of the firstsemiconductor to form a second base semiconductor electrode on the firstbase semiconductor electrode and the base on the collector.

[0018] According to the present invention, there is also provided abipolar device, comprising: an insulation film having a collector areaprovided with a vertical sidewall; a collector filled in the collectorarea and protruded over silicon nitride on a surface of a substrate tobe formed into a mushroom shape; an oxide film enclosing only a sideportion of a protruded portion of the collector; a first basesemiconductor electrode formed on the nitride insulation film at athickness corresponding to a height of the oxide film; a base contactedon the collector; and a second base semiconductor electrode extended toa side portion of the base and formed on the first base semiconductorelectrode.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is a cross-sectional view of a structure of a conventionalsilicon-germanium heterojunction bipolar transistor manufactured byLOCOS method;

[0020]FIG. 2 is a cross-sectional view of another conventionalsilicon-germanium heterojunction bipolar transistor manufactured by SEGmethod; and

[0021]FIGS. 3a to 3 i are cross-sectional views showing a method ofmanufacturing a silicon-germanium heterojunction bipolar transistoraccording to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] The objects, characteristics and advantages of theabove-described invention will become more apparent by describing thepreferred embodiments thereof with reference to the accompanyingdrawings.

[0023]FIGS. 3a to 3 h are cross-sectional views showing a method ofmanufacturing a silicon-germanium heterojunction bipolar transistoraccording to the present invention.

[0024] Ion-implanting an n-type impurity such as arsenic or phosphorusin a p-type silicon substrate 101 forms a buried collector 111. On anentire surface of the substrate on which the buried collector 11 isformed, there is formed an insulation film 117 of silicon nitride(Si3N4).

[0025] At this time, preferably, there is provided a further oxideinsulation film 217 before forming the silicon nitride to form theinsulation film 117 in which the oxide film and the nitride film arestacked (FIG. 3a).

[0026] The insulation film 117 and 217 is patterned to form a collectorarea for exposing a part of the buried collector 111. The collector areais formed with a vertical type sidewall 117 a. In the collector area, anintrinsic semiconductor containing p-type silicon grows by selectiveepitaxial growth (SEG) method. At this time, the intrinsic semiconductorexcessively grows over the collector area to form a mushroom-shapedcollector 115 protruded on the insulation film (FIG. 3b).

[0027] A heat treatment process oxidizes an upper surface of theprotruded collector 115 to form an oxide film 199 of silicon dioxide.Therefore, only the insulation film 117 of the silicon nitride and theoxide film 199 of the silicon dioxide covering the collector 115 areexposed on the surface of the substrate (FIG. 3c).

[0028] Out of the surfaces of the substrate comprised of the insulationfilm 117 of the silicon nitride and the oxide film 199 of the silicondioxide, polycrystalline silicon grows selectively on the insulationfilm 117 of the silicon nitride by SEG method to form a buffer layer122. In fact, there is a difference in growth selectivity of the siliconwhen it is grown on silicon nitride and silicon dioxide during the SEGprocess. Therefore, on the surface of the substrate, there aredistributed mainly the polycrystalline silicon and intermittently thesilicon dioxide (FIG. 3d).

[0029] Only the silicon dioxide is removed from the surface of thesubstrate covered by the polycrystalline silicon and the silicon dioxideso that an upper surface of the mushroom-shaped collector 115 is exposedand a side thereof is enclosed by the oxide film 199. Therefore, on thesurface of the substrate, there are distributed mainly thepolycrystalline silicon and intermittently the single crystallineintrinsic semiconductor. And also, a minimal portion of the oxide film199 is exposed on the surface of the substrate (FIG. 3e).

[0030] On the entire surface of the substrate mostly covered with thesilicon, a semiconductor material containing silicon-germanium grows byepitaxial growth method to form a base layer. Since the base layer onthe silicon grows under the same circumstances, the base layer is notinfluenced by loading effect and formed to have a uniform thickness overthe entire surface of the substrate. In addition, polycrystalline SiGegrows on the buffer layer 122 formed of the polycrystalline silicon toform a base electrode layer 123. On the upper portion of the collector115 enclosed by the oxide film 199, the single crystal SiGe grows toform a intrinsic base 125. A junction between the collector 115 and thebase 125 is defined not by a pattern using a mask but by the oxide film199 so as to be self-aligned. Therefore, since there is not absolutelyformed an overlapped area interposing the insulation film between thecollector 115 and the base 125 in the junction structure therebetween,junction parasitic capacitance is prevented (FIG. 3f).

[0031] The buffer layer 122 and the base electrode layer 123 arepatterned together to form a base electrode 123 a and the base 125 inthe form of an island. On the substrate, silicon dioxide or siliconnitride is deposited to form an emitter insulation film 137. Then, theemitter insulation film 137 covering the base 125 is patterned to openan emitter area. Meanwhile, the emitter insulation 137 and the collectorinsulation film 117 covering the buried collector 111 are patterned toexpose a part of the buried collector 111 (FIG. 3g).

[0032] Polycrystalline n-type silicon is deposited and patterned to forman emitter 135 in the opened emitter area and a collector electrode 119contacted with the exposed buried collector 111 (FIG. 3h).

[0033] On the entire surface of the substrate, the silicon dioxide isdeposited to form a protecting layer 177. The protecting layer 177 ispatterned to expose the emitter 135 and the collector electrode 119. Andthe protecting film 177 and the emitter insulation film 137 covering thebase electrode 123 a are patterned to expose a part of the baseelectrode 123 a. A metal such as Ti, W, Cu, Au, Al, Cr and so forth issputtered and patterned to form a base terminal 181 contacted with thebase electrode 123, an emitter terminal contacted with the emitter 135and a collector terminal 185 contacted with the collector electrode 119(FIG. 3i).

[0034] According to the present invention, the problem of the leakagecurrent and the loading effect generated when manufacturing bipolartransistor in which the collector is formed by the SEG method areprevented. Further, since the collector is formed at an upper portionthan the insulation film, though a defect lattice is generated betweenthe collector and the insulation film, a current of the base is directedconnected to the defective portion and thus the leakage current betweenthe collector and the base is prevented, thereby improving a reliabilityof the product. And since the junction between the collector and base isformed to be self-aligned, an overlapped portion interposing theinsulation film therebetween is prevented, thereby minimizing thejunction capacitance. Thus, the intrinsic area of the device isprecisely and finely formed. In addition, since the base film grows onthe silicon surface of the substrate, the base film is not affected bythe loading effect and formed to have a uniform thickness, therebyincreasing a performance of the product.

[0035] Although the preferred embodiment of the present invention havebeen disclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

What is claimed is:
 1. A method of manufacturing a bipolar device, inwhich a collector, a base and an emitter are formed in order, comprisingsteps of: (a) depositing an insulation film containing silicon nitrideon a substrate and removing a part of the insulation film to define acollector area; (b) growing a first semiconductor in the collector areaby selective epitaxial growth method to form the collector protrudedover the insulation film in the form of a mushroom; (c) forming an oxidefilm containing silicon dioxide on a surface of the collector protrudedover the silicon nitride; (d) selectively growing a secondpolycrystalline semiconductor material on only the nitride insulationfilm at the same height as the protruded portion of the collector toform a first base semiconductor electrode; (e) removing an upper surfaceof the oxide film to expose the collector; and (f) growing a secondsemiconductor containing silicon-germanium on the second polycrystallinesemiconductor and the collector of the first semiconductor to form asecond base semiconductor electrode on the first base semiconductorelectrode and the base on the collector.
 2. The method of claim 1,wherein the substrate comprises a buried collector, in which a firstimpurity is ion-implanted, on the substrate containing the secondsemiconductor, and a part of a surface of the buried collector isexposed through the collector area.
 3. The method of claim 1, furthercomprising a step of (g) depositing and patterning an insulationmaterial on the base and the second base semiconductor electrode to forman emitter insulation film for exposing the most part of the base.
 4. Abipolar device, comprising: an insulation film having a collector areaprovided with a vertical sidewall; a collector filled in the collectorarea and protruded over silicon nitride on a surface of a substrate tobe formed into a mushroom shape; an oxide film enclosing only a sideportion of a protruded portion of the collector; a first basesemiconductor electrode formed on the nitride insulation film at athickness corresponding to a height of the oxide film; a base contactedon the collector; and a second base semiconductor electrode extended toa side portion of the base and formed on the first base semiconductorelectrode.
 5. The bipolar device of claim 4, wherein the nitrideinsulation film is formed on a buried collector comprising the substratecontaining a first semiconductor and a semiconductor containing a secondimpurity in the substrate, and a part of the buried collector is exposedthrough the collector area.
 6. The device of claim 4, furthercomprising: an emitter insulation covering the second base semiconductorelectrode and exposing the most part of the base; and an emittercontacted with the exposed base portion.